Long-term changes in air-sea heat fluxes in the North Atlantic: Toward a latitudinal reorganization of the ocean heat budget

Abstract

This study analyzes the ocean heat budget (OHB) in the eastern North Atlantic (0^°–60^° N, 20^° W) using monthly ERA5 data from 1980 to 2024. The four main surface fluxes—short-wave and long-wave radiation, latent and sensible heat—were examined to characterize meridional and seasonal variability, detect long-term trends, and identify their physical drivers. The OHB shows a three-zone structure: a tropical heat sink (0–20^° N) dominated by short-wave input up to +250 ± 35 W m⁻²; a subtropical transition zone (20–40^° N) where latent heat loss peaks near 30^° N (∼ − 130 ± 23 W m⁻²); and a subpolar heat source (40–60^° N) driven by wintertime turbulent fluxes exceeding −150 ± 48 W m⁻². Between 1980 and 2024, sea-surface temperature rose by ∼ 0.27 ± 0.05 °C dec⁻¹ and specific humidity by ∼ 0.20 ± 0.04 g kg⁻¹ dec⁻¹.

Latent-heat flux trends reached +2.5 ± 1.1 W m⁻² dec⁻¹ in the subtropics, while sensible-heat flux decreased by ∼ 1 ± 0.22 W m⁻² dec⁻¹ north of 50^° N. These contrasting tendencies indicate a latitudinal reorganization of air–sea heat exchange: enhanced evaporative cooling near 30^° N and reduced winter heat loss at subpolar latitudes. Net short-wave radiation remains the main contributor to the OHB (32 ± 7–62 ± 5%), while latent heat flux drives most of the variability. Together, the results point to a progressive redistribution of ocean heat under ongoing climate change.